Hot pressing of boron carbide with silicon carbide additives (5 – 25 wt.%) leads to the formation of a composite material, the matrix phase of which is close in stoichiometry to boron carbide, but contains a small amount of silicon, which can partially replace carbon or boron in chains binding boron icosahedrons in the structure, because the covalent atomic radii Si, B and C are close. This may explain the higher mechanical properties of the composite material B4C – 22 wt.% SiC compared to the properties of sintered boron carbide without additives. When adding 20 wt.% SiC to the initial mixture, the approximate stoichiometry of the matrix phase of the material sintered at 30 MPa, 2200 C, 5 min., was B3.64CSi0.01 and contained the inclusion with approximate stoichiometry SiC1.07, and the density of material was = 2.63 g/cm3. According to X-ray diffraction analysis, the material contained 78 wt.% B4C and 22 wt.% SiC – 6H, and its mechanical characteristics were as follows: HV (9.8 N) = 51.7 ± 12.8 GPa, HV (49 N) = 34.6 ± 0.5 GPa and K1C (49 N) = 5.4 ± 1.1 MPa•m0.5, flexural strength σb = 474 MPa, compressive strength σc = 1878 MPa; the addition of more (25 wt.%) or less (15 wt.%) SiC and reducing of the synthesis temperature to 2050 C led to a deterioration of mechanical properties due to greater porosity or less dissolution of silicon in the structure of boron carbide. Numerical simulation of multi-layer ceramic protection elements (composition 22% B4C + 78% SiC) with a 12 mm bullet was performed. Central and peripheral shocks for plates of rounded cylinders are considered. The change in time of the stress state of the elements and the conditions of loss of the destructive ability of the bullet are analyzed. Based on the simulation results, the design parameters of security elements are optimized.
The investigation was performed in the frames of the Projects NATO SPS G5773 and Project III-3-20 (0779) supported by the NAS of Ukraine.
2022-04-06 08:00:00
